1. Field of the Invention
The invention relates generally to the art of forming cup-shaped members such as metal containers from a blank of metal such as aluminum, steel, tin or other suitable material. More particularly, the invention relates to the formation of such metal containers in a single-acting press or a double-acting press which includes a vertically stacked arrangement of pistons having one or more damping members which reduce forces exerted on the pistons and also on the press by continuously increasing the pneumatic clamping force exerted on the metal blank when drawing the metal container.
2. Background Art
Cup-shaped members formed from metal have become popular for packaging food, such as beverages and moist pet foods, as well as other materials. These cups-shaped members are typically formed from a blank of metal using either a single-acting press or a double-acting press. More particularly, the cup-shaped member is formed by stamping a disk-shaped blank from a metal sheet. This disk-shaped blank is then drawn into the desired cup-like configuration. Following formation of the cup-shaped members, each of the members is filled with a predetermined quantity of food or other suitable product and are fitted with a metal lid or end closure. The lid is fixedly attached to the cup-shaped member using a separate process which crimps the lid onto the upper open portion of the cup-shaped member. The lid or end closure typically is formed with a pop-top or tab which provides the end user a relatively easy means for opening the cup-shaped member.
Cup-shaped members, like those described above, are typically formed in either a single-acting press or a double-acting press. Both single and double-acting presses for forming cup-shaped members are well known in the art. Although particular designs may vary, a typical single or double-acting press design cuts and draws the cup-shaped member in a single stroke of the press. More specifically, in these types of presses, the blank is cut from a metal sheet and is subsequently drawn into its final cup-shaped configuration in one single stroke of the press. Both single-acting presses and double-acting presses include multiple cut and forming dies which are capable of simultaneously forming a plurality of cup-shaped members, such as ten, twelve, or more cup-shaped members in a single stroke of the press. Because the present invention is capable of being used in conjunction with either a single-acting or a double-acting press, the general structure and operation of both presses is set forth below.
A single-acting press typically includes a single ram and a base. The single ram cuts and holds the blank from the sheet of material and also draws the blank into its final cup-shaped configuration. Of particular importance to the single-acting press is the pressure piston system which is carried on the single ram. The pressure piston system consists of a plurality of stacked pistons each of which is mounted within a respective cylinder which is in turn carried on the single ram of the press. As the single ram moves downwardly, it captures a portion of the metal sheet, cuts it into a blank, and clampingly engages the outer perimeter of the blank to the blank and draw die which is mounted on the base of the press. As the single ram continues to move downwardly, a draw horn draws the blank into a cup-shaped member as the pressure piston system continues to clampingly engage the outer edge of the blank.
A double-acting press typically includes an inner ram and an outer ram. The outer ram cuts and holds the blank from a sheet of material while the inner ram draws the blank into its final cup-shaped configuration. Of particular importance to the double-acting press, and more specifically the outer ram of the double-acting press, is the piston pressure system which is carried on the outer ram. This piston pressure system consists of a plurality of stacked pistons each of which is mounted within a respective cylinder which is in turn carried on the outer ram of the press. As the outer ram is moved downwardly, it captures a portion of the metal sheet, cuts it into a blank, and clampingly engages the outer perimeter of the blank to the blank and draw die which is mounted on the base of the press. The inner ram, which carries a draw horn, then moves downwardly through the annular space within the outer ram to draw the blank into a cup-shaped member as the outer ram clampingly engages the outer edge of the blank during the draw stage.
In this arrangement for both the single-acting and double-acting press, the pistons simultaneously engage one another resulting in a clamping pressure on the outer edge of the blank of about 6,000 pounds. In a typical single or double-acting press setup, there are three pistons, each of which are mounted within a respective one of three cylinders, each piston capable of exerting about 2,000 pounds of clamping pressure. Because the pistons are engaged simultaneously, an instantaneous application of the full 6,000 pound clamping load is imparted on the outer perimeter of the blank and the blank and draw die which is mounted on the base of the press. This instantaneous 6,000 pound clamping load can potentially cause excessive wear on the pistons as well as the blank and draw die mounted on the base of the press, which in turn can cause the pistons and the blank and draw die to fail prematurely. In addition, these large instantaneous forces can also potentially cause excessive noise and vibration in the press itself, which can in turn potentially lead to premature wear and ultimately possible failure of the press.
Therefore, a need exists in the art for a cup-shaped member forming apparatus which includes a pressure piston system design that reduces the effects of applying an instantaneous large clamping force on the blank material and the blank and draw die mounted on the base of the press in either a single or double-acting press, which can potentially cause excessive wear on the pistons and which potentially can lead to premature failure of the pistons and the press, while still reducing excessive noise and vibration in the press in order to decrease wear on the press.
These improvements are provided by the apparatus for forming cup-shaped members of the present invention, which includes a pressure piston system having an arrangement of stacked pistons which include one or more damping members that provide a continuous increase in clamping pressure exerted by the draw pad on the blank and draw die mounted on the base of the press in order to reduce the effects of applying an instantaneous clamping pressure on the pistons and to reduce wear on the pistons as well as reducing noise and vibration in the press.